Origin

Early use of the word was as a synonym for assize, of which it is a shortening. This came from French assise, from Latin assidere ‘sit by’ which developed the sense ‘to sit down in judgement, assess’ of which it is also the source. The notion of fixing an amount led to the word's use to express magnitude and bulk. The phrase size up appeared in the late 19th century. The history of the size (Middle English) used in painting is not clear. See also seat

Origin

Early use of the word was as a synonym for assize, of which it is a shortening. This came from French assise, from Latin assidere ‘sit by’ which developed the sense ‘to sit down in judgement, assess’ of which it is also the source. The notion of fixing an amount led to the word's use to express magnitude and bulk. The phrase size up appeared in the late 19th century. The history of the size (Middle English) used in painting is not clear. See also seat